1. Field of the Invention
This invention relates to a cantilever type probe to be used for scanning tunneling microscope (hereinafter abbreviated as STM) and so forth and a scanning tunnelling microscopy equipped with such probe.
Further, the present invention relates to a cantilever type probe which performs recording, reproduction and erasing, etc. of information according to the method of STM, and an information processing device equipped with the same.
2. Related Background Art
In recent years, scanning tunneling microscope (hereinafter abbreviated as STM) which can observe directly the electron structure of surface atoms of a conductor has been developed (G. Binnig et al., Phys. Rev. Lett. 49 (1982) 57), whereby real space image can be measured with remarkably high resolving power (nanometer or less) irrespectively of whether it may be single crystal or amorphous. STM utilizes the phenomenon that a current flows when a voltage is applied between a metal tip and an electrically conductive substance and distance between the both approaches about 1 nm. Since the current is very sensitive to the distance change between the both and will change exponentially, the surface structure of the real space can be observed with a resolving power of the atomic order by scanning the tip so as to maintain constantly the tunnel current. Analysis by use of STM is limited to electrically conductive materials, but it has now begun to be applied to the structural analysis of the insulation film formed thinly on the surface of electrically conductive materials. Further, because such device and means utilize the method of detecting minute current, they have also the advantage that no damage is given to the medium, and also observation can be made with low power. Also, since actuation in the air is also possible, a wide scope of application of STM has been expected.
Particularly, as proposed in Japanese Laid-open Patent Applications Nos. 63-161552, 63-161553, practical application as high density recording and reproduction device has been positively progressed. This performs recording by varying the voltage applied between the probe and the recording medium by use of the same probe as STM, and as the recording medium, materials exhibiting switching characteristics having memory characteristic in voltage-current characteristics, for example, thin film layers of chalocogenides, .pi.-electron system organic compounds have been used. Reproduction is performed by the change in tunnel resistance between the region where recording is done and the region where no recording is done. As the recording medium for this recording system, recording and reproduction may be possible even on such medium with the surface shape of the recording medium being changed by the voltage applied on the probe.
When the operation of the STM or recording and reproduction applying STM are to be performed, important are the two points of controlling the distance between the probe and the sample or the recording medium on the .ANG. order, and, in recording and reproduction, controlling the two-dimensional scanning of the probe on the several 10.ANG. order for recording and reproducing the information arranged two-dimensionally on the medium. Further, from the standpoint of functional improvement of the recording and reproduction system, particularly acceleration of speed, it has been proposed to drive a large number of probes at the same time (multi-formation of probes). Shortly speaking, the relative position of the probe and the medium must be controlled three-dimensionally with the above precision within the area where a large number of probes are arranged.
In the prior art, for such control, lamination type piezoelectric elements, cylinder type piezoelectric elements, etc. mounted on the probe side or the medium side have been used. However, these elements, while they can take large displacement amounts, are not suitable for integration, and can be disadvantageously used for a multi-probe type recording and reproduction device. From this standpoint, the method of mounting the probe on a cantilever with a length of several 100 .mu.m and driving the cantilever with a piezoelectric material has been considered.
In the prior art, as the preparation method of such cantilever, there is the method of preparing a cantilever having a multi-layer structure of piezoelectric material thin films, metal films, etc. according to the working technique to make a fine structure on one substrate by use of the semiconductor preparation process technique (T. R. Albrecht et al. "Microfabrication of integrated Scanning Tunneling microscope", Proceedings Fourth International conference on scanning tunneling microscopy/spectroscopy, 1989).
FIG. 4 shows a sectional view of the cantilever type probe of a prior art example. 101, 102 are piezoelectric material thin films, 103-107 are electrodes for driving piezoelectric materials, 108-111 dielectric material films, 112 a tip, and 113 an electrode for drawing out withdrawal. FIG. 5 shows a block diagram of the STM device by use of the cantilever type probe. 201 is a power source for bias application, 202 a tunnel current amplification circuit, 203 a driver for cantilever driving, 204 a cantilever, 205 a tip and 206 a sample. Here, by detecting the tunnel current I.sub.t flowing between the tip 205 and the sample 206, applying a feedback so that I.sub.t may be constant and driving the cantilever 204, the interval between the tip 205 and the sample 206 is maintained. FIG. 6 shows the equivalent circuit of the above STM device. I.sub.t is tunnel current, E bias power source, R.sub.i bias power internal resistance, R.sub.T tunnel resistance, V.sub.1 power source for cantilever driving, R.sub.i ' internal resistance, C.sub.1 floating capacitance existing between driving electrode and substrate, R.sub.1 substrate resistance, C.sub.2 capacitance according to the constitution having the piezoelectric material thin film sandwiched between driving electrodes, R.sub.2 resistance of the piezoelectric material, C.sub.3 floating capacity existing between the electrode for drawing out and the driving electrode, R.sub.3 its resistance, V.sub.2 the electromotive force due to the piezoelectric effect of the piezoelectric material displaced by V.sub.1, which may be considered to be V.sub.2 --V.sub.1. C.sub.4 is the capacitance according to the constitution having the piezoelectric material thin film sandwiched between the electrode for drawing out and the driving electrode, and R.sub.4 the resistance of that portion.
In the above prior art example, during tunnel current detection, the noise sources will be the current flowed in from C.sub.2, R.sub.2 portions and the current flowed in from V.sub.2, C.sub.4, R.sub.4 portions in FIG. 6. Generally speaking, C.sub.2 is not a lamination type so it has a small value, while R.sub.2 is large, and therefore V.sub.2, C.sub.4 are substantially problems. Particularly, they are problems when the thickness of the laminated body constituting the cantilever is made small. For example, when the driving frequency is made 1 kHz at V.sub.1 =.+-.5 V for driving the cantilever, and the cantilever length 1 mm, the piezoelectric material film thickness 1 .mu.m, the width of the electrode for drawing out probe 20 .mu.m, V.sub.2 becomes ca. .+-.5 V, 1 kHz, C.sub.4 ca. 1 pF, and the noise current I.sub.n becoming In=C.sub.4 .times.dV.sub.2 /dt ca. 20 nA. Ordinarily, since I.sub.t = about 10 pA to 10 nA in STM device, such I.sub.n makes detection of tunnel current based on the sample information difficult. Particularly, in the recording and reproduction device by use of a cantilever type probe, high speed driving is required and hence the influence from C.sub.4 is more serious.
Also, by use of the method of STM, there have been made studies about applications to various fields of observation evaluations, fine working of semiconductors or high molecular weight materials, etc. on the atomic order, molecular order (E. E. Ehrichs, 4th International Conference on Scanning Tunneling Microscopy/spectroscopy, '89, S13-3), and recording devices, etc.
Among them, in calculation information of computer or picture information, demands for recording devices having larger capacity are increasingly higher, and further because of calculation ability of the microprocessor which has been made smaller in size due to the progress of the semiconductor process technique, the recording device has been desired to be made smaller in size.
For the purpose of satisfying these demands, there has been proposed a recording and reproduction device with the minimum recording area of 10 nm square, which performs writing of a record by changing the work function of the recording medium surface by applying a voltage from a transducer comprising a probe for tunnel current generation existing on the driving means capable of fine control of the interval with the recording medium, and also performs reading of the information by detecting the change in tunnel current by the change in work function.
In such device, for improvement of transfer of information and recording speed, for example, it is required to increase the number of probes and permit them to run on the recording data series, while controlling the interval between the probes and the medium. However, the width of the data series recorded is very fine, and due to the influences of the drift by the temperature change of the device, or the vibration from the outside, etc., the probes will come off from the data series to make stable recording and reproduction impossible. Further, when one probe is scanned along the data series, other probes will come off from the data series.